Centrifugal pumping apparatuses are widely used for pumping liquids. The centrifugal pump typically includes an impeller which is connected to one end of a rotary shaft which is rotatably driven by an electric motor, steam turbine, or other prime mover. The impeller is housed within an impeller casing. Fluid entering the casing at the center of the impeller is radially displaced and pressurized by the rotating impeller. The pressurized fluid then exits the casing via an outlet located along the periphery of the casing. Connected to the casing is a pump housing having a bearing housing that rotatably supports the rotary shaft extending through an aperture between the pump housing and the impeller casing.
Fluid pumped within the impeller casing must be prevented from flowing rearward along the rotating shaft, through the aperture between the pump housing and impeller casing, toward the motor and leaking into the environment. The sealing about the rotating shaft in a centrifugal pump is frequently accomplished with dynamic seals, compressive stuffing or mechanical seals. The stuffing or seal is inserted in a stuffing chamber or box formed between the shaft and the pump housing rearward of the impeller.
When the pump is handling clear liquids, fibrous slurries, liquids with suspended solids and other fluids, a dynamic seal is frequently used to seal about the rotating shaft. A repeller is housed in a repeller chamber formed between the pump housing forward of the stuffing box and a backplate inserted between the impeller casing and pump housing. The repeller chamber is in communication with the fluid in the impeller casing.
The repeller is rotatably attached to the shaft and includes a radial disk with a smooth forward surface facing the backplate, and a number of radially extending vanes integrally attached to the rearward surface of the disk. As the fluid is pumped through the impeller casing, the fluid enters the repeller chamber and travels radially outward between the backplate and the smooth surface of the rotating disk. Due to the viscous drag between the smooth surface of the rotating disk and fluid, a vortex is formed in the fluid between the disk and backplate.
As the fluid begins to migrate radially inward along the rearward surface of the disk, the pumping action of the rotating vanes creates a pressure rise in the fluid which prevents the fluid from reaching the shaft.
One of the drawbacks of the use of prior repellers is that when the fluid contains dispersed solid material such as a fibrous slurry which has a fiber content of about 3.0% or greater, depending upon the type of slurry, the centrifugal forces in the vortex and the specific gravity of the fibers cause the dispersed fibers in the slurry to begin to clot in the repeller chamber about the repeller. This clotting is known as dewatering of the slurry, and the dewatered slurry interferes with the action of the pump. Previously, passing liquid through or flushing of the repeller chamber was required to remove the clot of fibers in the slurry, thereby causing auxiliary equipment to be included with the pump.
Therefore, it is a primary object of the present invention to provide a repeller and repeller chamber for a centrifugal pumping apparatus for handling fibrous slurries which applies shear forces to the fluid vortex created by the repeller action to create circulatory flow within the vortex and maintain the dispersion of the fibrous material in the slurry.
Another object of the present invention is to provide a repeller and repeller chamber for a centrifugal pumping apparatus for handling fibrous slurries which includes scalloped indentations in the circumference of a radial disk forming the repeller wherein the scalloped indentations, and the degree of linear depth of the scalloped indentations, create shear forces in the vortex formed in the fluid passing between the repeller and the repeller chamber to prevent dewatering of the fibrous material and to prevent plugging of the repeller or repeller chamber by the fibrous material.
A further object of the present invention is to provide a repeller and repeller chamber for a centrifugal pumping apparatus for handling fibrous slurries which include a plurality of inwardly extending stationary radial vanes spaced around the annular surface of the repeller chamber, and the dimensional relationship between the stationary radial vanes of the repeller chamber and the radial extent of the vanes formed on the repeller creates shear forces in the fluid vortex in the repeller chamber.
Another object of the present invention is to provide a repeller and a repeller chamber in a centrifugal pump for handling fibrous slurries which includes the presence of recirculation zones disposed between the repeller chamber annular surface and the repeller to provide acceleration of the fluid flow at the upstream side of stationary ribs found in the repeller chamber, thereby creating shear forces in the vortex within the repeller chamber.